Deposition of Oil Shale in the Fushun Basin, Eocene, N-E China

The Fushun Basin (NE China) is located along the Dunhua-Mishan fault zone. This lacustrine strike-slip basin hosts the largest open pit coal and oil shale mine in Asia. Oil shales overlying sub-bituminous coal occur within the middle Eocene Jijuntun Formation. The main aim of the study was to reconstruct the depositional environment of the oil shales. Furthermore, the source rock potential was evaluated. A total of 50 samples from the West Open Pit mine were studied using Rock Eval pyrolysis, Leco, biomarker and maceral analysis. The results show that the oil shale was deposited in a tectonically controlled freshwater lake, which originated after drowning of a peat. Organic matter rich sediments with TOC contents up to 23.6 wt.% containing kerogen type I (formed by bacteria and algae) were deposited under anoxic conditions in the upper part of the Jijuntun Formation, probably caused by temperature stratification of the water column. We speculate that this water column stratification was supported by increasing depth of the lake during oil shale deposition. Landplants and aquatic organisms are abundant in the lower part of the Jijuntun Formation. The amount of landplants decreases upwards.